实验任务
实验目的
扩展板卡上集成了1.8寸彩色液晶屏TFT_LCD模块,大家可以驱动LCD显示文字、图片或动态的波形。本实验主要学习1.8寸串行彩色液晶屏的驱动设计,然后将小脚丫Logo处理显示,完成图片显示系统的总体设计。
本文引用地址:设计框图
根据前面的实验解析我们可以得知,该设计可以拆分成两个功能模块实现,
实验原理
液晶屏介绍
查看底板上集成的1.8寸串行彩色液晶屏规格书,屏幕采用ST7735S的驱动芯片,接下来我们主要根据ST7735S的芯片手册来了解其工作原理和驱动方法。
ST7735S为132RGB x 162像素点 262K 控制器/驱动器,芯片可以直接跟外部处理器连接,支持串行SPI通信和8/9/16/18位并行通信(本液晶屏集成ST7735S时没有留并行接口,所以只能使用串行通信),详细参数请参考数据手册。
ST7735S支持不同位宽的并行通信格式。
在控制器给屏幕刷屏时,根据MV、MX、MY的配置支持8种不同方向的刷屏模式。
支持大量功能指令,部分系统功能指令列表如下
更多的内容这里就不一一介绍了,感兴趣的同学可以详细阅读ST7735S芯片手册。
液晶屏硬件连接
底板上的1.8寸串行彩色液晶屏模块电路:
底板上的1.8寸串行彩色液晶屏电路和VGA显示电路复用部分FPGA管脚,两者不能同时使用,当使用1.8寸串行彩色液晶屏时,DISPSEL信号置高,驱动1.8寸串行彩色液晶屏使能同时点亮背光,DISP2~ DISP_5分别对应RESET、D/C、SDA、SCK管脚,最后FPGA驱动1.8寸液晶屏完成屏显示控制即可。
液晶屏驱动设计
要驱动液晶屏需要先了解液晶屏的驱动流程,可以从液晶屏驱动芯片ST7735S的芯片手册上获取,也可以到网上找找有没有别人使用同类液晶屏的案例,或者向卖方问问有没有相关资料提供,这里我们找到了一个用51单片机驱动的程序例程,例程仅供参考,需要根据例程中的配置到芯片手册中查找确认,不可以直接套用。
首先完成液晶屏初始化操作,51程序流程如下:
void ST7735_LAIBAO177_INITIAL () { //-----------ST7735R Reset Sequence----------------// RES =1; delay (1); //Delay 1ms RES =0; delay (1); //Delay 1ms RES =1; delay (120); //Delay 120ms //----------End ST7735R Reset Sequence ------------// LCD_WriteCommand(0x11); //Sleep out delay(120); //Delay 120ms //---------ST7735S Frame Rate-------------------// LCD_WriteCommand(0xB1); LCD_WriteData(0x05); LCD_WriteData(0x3C); LCD_WriteData(0x3C); LCD_WriteCommand(0xB2); LCD_WriteData(0x05); LCD_WriteData(0x3C); LCD_WriteData(0x3C); LCD_WriteCommand(0xB3); LCD_WriteData(0x05); LCD_WriteData(0x3C); LCD_WriteData(0x3C); LCD_WriteData(0x05); LCD_WriteData(0x3C); LCD_WriteData(0x3C); //-----------End ST7735S Frame Rate---------------// LCD_WriteCommand(0xB4); //Dot inversion LCD_WriteData(0x03); //-----------ST7735S Power Sequence---------------// LCD_WriteCommand(0xC0); LCD_WriteData(0x28); LCD_WriteData(0x08); LCD_WriteData(0x04); LCD_WriteCommand(0xC1); LCD_WriteData(0XC0); LCD_WriteCommand(0xC2); LCD_WriteData(0x0D); LCD_WriteData(0x00); LCD_WriteCommand(0xC3); LCD_WriteData(0x8D); LCD_WriteData(0x2A); LCD_WriteCommand(0xC4); LCD_WriteData(0x8D); LCD_WriteData(0xEE); //----------End ST7735S Power Sequence----------// LCD_WriteCommand(0xC5); //VCOM LCD_WriteData(0x18); //1a LCD_WriteCommand(0x36); //MX, MY, RGB mode LCD_WriteData(0xC0); //-----------ST7735S Gamma Sequence-----------// LCD_WriteCommand(0xE0); LCD_WriteData(0x04); LCD_WriteData(0x22); LCD_WriteData(0x07); LCD_WriteData(0x0A); LCD_WriteData(0x2E); LCD_WriteData(0x30); LCD_WriteData(0x25); LCD_WriteData(0x2A); LCD_WriteData(0x28); LCD_WriteData(0x26); LCD_WriteData(0x2E); LCD_WriteData(0x3A); LCD_WriteData(0x00); LCD_WriteData(0x01); LCD_WriteData(0x03); LCD_WriteData(0x13); LCD_WriteCommand(0xE1); LCD_WriteData(0x04); LCD_WriteData(0x16); LCD_WriteData(0x06); LCD_WriteData(0x0D); LCD_WriteData(0x2D); LCD_WriteData(0x26); LCD_WriteData(0x23); LCD_WriteData(0x27); LCD_WriteData(0x27); LCD_WriteData(0x25); LCD_WriteData(0x2D); LCD_WriteData(0x3B); LCD_WriteData(0x00); LCD_WriteData(0x01); LCD_WriteData(0x04); LCD_WriteData(0x13); //------------End ST7735S Gamma Sequence----------// LCD_WriteCommand(0x3A); //65k mode LCD_WriteData(0x05); LCD_WriteCommand(0x29); //Display on }
创建存储器,将初始化过程中写的所有指令和数据存储,同时存储的还有指令或数据标志,例如初始化第1条指令为8'h11,我们增加最高位1‘b0组成9位位宽数据。存储器部分指令和数据如下:
initial begin //LCD初始化的命令及数据 reg_init[ 0] = {1'b0,8'h11}; //最高位为0,表示低8位为指令 reg_init[ 1] = {1'b0,8'hb1}; reg_init[ 2] = {1'b1,8'h05}; //最高位为1,表示低8位为数据 reg_init[ 3] = {1'b1,8'h3c}; reg_init[ 4] = {1'b1,8'h3c};
从51例程中可以看到,整个初始化过程都在给液晶屏写指令或数据,通过查看写指令或写数据的时序发现,唯一不同的就是对A0(对应底板液晶屏模块中的D/C信号)的控制,程序实现如下:
void LCD_WriteXXX(uint dat) { int i; A0=0; //写指令,如果写数据 A0=1; CSB=0; //液晶屏使能 for(i=0;i<8;i++) { if(dat &0x80) SDA=1; else SDA=0; SCL=0; SCL=1; dat <<=1; } CSB=1; }
FPGA驱动液晶屏的设计使用状态机完成,将写数据与写指令的SPI时序整合成一个状态,另加一位指令数据控制位,程序实现如下:
WRITE:begin //WRITE状态,将数据按照SPI时序发送给屏幕 if(cnt_write >= 6'd17) cnt_write <= 1'b0; else cnt_write <= cnt_write + 1'b1; case(cnt_write) 6'd0: begin lcd_dc <= data_reg[8]; end //9位数据最高位为命令数据控制位 6'd1: begin lcd_clk <= LOW; lcd_din <= data_reg[7]; end //先发高位数据 6'd2: begin lcd_clk <= HIGH; end 6'd3: begin lcd_clk <= LOW; lcd_din <= data_reg[6]; end 6'd4: begin lcd_clk <= HIGH; end 6'd5: begin lcd_clk <= LOW; lcd_din <= data_reg[5]; end 6'd6: begin lcd_clk <= HIGH; end 6'd7: begin lcd_clk <= LOW; lcd_din <= data_reg[4]; end 6'd8: begin lcd_clk <= HIGH; end 6'd9: begin lcd_clk <= LOW; lcd_din <= data_reg[3]; end 6'd10: begin lcd_clk <= HIGH; end 6'd11: begin lcd_clk <= LOW; lcd_din <= data_reg[2]; end 6'd12: begin lcd_clk <= HIGH; end 6'd13: begin lcd_clk <= LOW; lcd_din <= data_reg[1]; end 6'd14: begin lcd_clk <= HIGH; end 6'd15: begin lcd_clk <= LOW; lcd_din <= data_reg[0]; end //后发低位数据 6'd16: begin lcd_clk <= HIGH; end 6'd17: begin lcd_clk <= LOW; state <= DELAY; end // default: state <= IDLE; endcase end
初始化指令和数据都放到存储器中了,数据写入的SPI串行时序也已经设计成了一个状态,初始化状态只需要在复位后将存储器中的指令或数据通过WRITE状态发送给液晶屏,程序实现如下:
INIT:begin //初始化状态 if(cnt_init==3'd4) begin if(cnt==INIT_DEPTH) cnt_init <= 1'b0; else cnt_init <= cnt_init; end else cnt_init <= cnt_init + 1'b1; case(cnt_init) 3'd0: lcd_res <= 1'b0; //复位有效 3'd1: begin num_delay<=16'd3000; state<=DELAY; state_back<=INIT; end 3'd2: lcd_res <= 1'b1; //复位恢复 3'd3: begin num_delay<=16'd3000; state<=DELAY; state_back<=INIT; end 3'd4: if(cnt>=INIT_DEPTH) begin //当62条指令及数据发出后,配置完成 cnt <= 16'd0; state <= MAIN; end else begin cnt <= cnt + 16'd1; data_reg <= reg_init[cnt]; if(cnt==16'd0) num_delay <= 16'd50000; //第一条指令需要较长延时 else num_delay <= 16'd50; state <= WRITE; state_back <= INIT; end default: state <= IDLE; endcase end
初始化完成,进入刷屏状态,刷屏数据写入前首先进行区域坐标的定位,然后刷写数据,图片采用单色显示,图片ram中每位数表示一个液晶屏一个像素点的亮还是灭,彩色液晶屏本实验采用16bit格式,即需要16bit数据决定像素的颜色,16bit数据分两次发送,最终从ram模块中获取的数据每位数据都要转换成16bit的数据,0转换成背景色对应的数据,1转换成顶层色对应的数据,程序实现如下:
SCAN:begin //刷屏状态,从RAM中读取数据刷屏 case(cnt_scan) 3'd0: if(cnt >= 11) begin //确定刷屏的区域坐标,这里为全屏 cnt <= 16'd0; cnt_scan <= cnt_scan + 1'b1; end else begin cnt <= cnt + 16'd1; data_reg <= reg_setxy[cnt]; num_delay <= 16'd50; state <= WRITE; state_back <= SCAN; end 3'd1: begin ram_clk_en<=HIGH;ram_addr<=y_cnt;cnt_scan<=cnt_scan+1'b1; end 3'd2: begin cnt_scan <= cnt_scan + 1'b1; end //延时一个时钟 3'd3: begin ram_clk_en<=LOW;ram_data_r<=ram_data;cnt_scan<=cnt_scan+1'b1; end 3'd4: begin //每个像素点需要16bit的数据,SPI每次传8bit,两次分别传送高8位和低8位 if(x_cnt>=LCD_W) begin //当一个数据(一行屏幕)写完后, x_cnt <= 8'd0; if(y_cnt>=LCD_H) begin y_cnt <= 8'd0; cnt_scan <= cnt_scan + 1'b1; end //如果是最后一行就跳出循环 else begin y_cnt <= y_cnt + 1'b1; cnt_scan <= 3'd1; end //否则跳转至RAM时钟使能,循环刷屏 end else begin if(high_word) //根据相应bit的状态判定显示顶层色或背景色,根据high_word的状态判定写高8位或低8位 data_reg <= {1'b1,(ram_data_r[x_cnt]? color_t[15:8]:color_b[15:8])}; else begin data_reg <= {1'b1,(ram_data_r[x_cnt]? color_t[7:0]:color_b[7:0])}; x_cnt <= x_cnt + 1'b1; end // high_word <= ~high_word; //high_word的状态翻转 num_delay <= 16'd50; //设定延时时间 state <= WRITE; //跳转至WRITE状态 state_back <= SCAN; //执行完WRITE及DELAY操作后返回SCAN状态 end end 3'd5: begin cnt_scan <= 1'b0; state <= MAIN; end default: state <= IDLE; endcase end
系统总体实现
液晶屏驱动模块的数据来源于图片数据的ram模块,这些数据由图片取模得到,使用图片取模软件,将图片载入软件,输出数据类型选择C语言数组,根据液晶屏驱动实际情况配置对应的扫描模式,输出灰度选择单色,调整最大宽度和高度符合液晶屏要求,最后点击保存生成需要的文件。
打开生成的文件,数据格式如下,是C语言的格式
const unsigned char gImage_11[1990] = { 0X10,0X01,0X00,0X80,0X00,0X7C, 0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00, 0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00, 0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00, 0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0XF8,0X00,0X00,0X00,0X00,0X00,0X00,0X00, 0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X07,0XFF,0X00,0X00,0X00,0X00,0X00,0X00,0X00,
使用编辑器的查找替换功能,将数据处理成下图格式
132'h00000000000000000000000000000000, 132'h00000000000000000000000000000000, 132'h00000000000000000000000000000000, 132'h0000000000000000F800000000000000, 132'h0000000000000007FF00000000000000,
创建ram模块,将图片数据初始化到ram中,程序实现图下:
module LCD_RAM (input wire [7:0] Address, output reg [131:0] Q); always @ (*) case(Address) 8'd0 : Q = 132'h00000000000000000000000000000000; 8'd1 : Q = 132'h00000000000000000000000000000000; 8'd2 : Q = 132'h00000000000000000000000000000000; 8'd3 : Q = 132'h0000000000000000F800000000000000; 8'd4 : Q = 132'h0000000000000007FF00000000000000;
存储图片数据的ram本实验采用分布式ram搭建,前面波形信号发生器实验中讲过ram IP核的例化及使用方法,有兴趣的同学可以自己尝试一下。
在顶层模块中,将两个模块例化并连接,最终完成图片显示系统的总体设计。
实验步骤
实验现象
将设计加载到FPGA中,观察底板液晶屏显示,小脚丫的Logo被显示出来了,前面说了1.8寸串行液晶屏支持不同的刷新方向,大家可以调整图片显示的方向
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